anyone got one of these? I'm trying to find out if a USB2 external enclosure that houses SATA drives would be as fast as having the drives internal to the machine. I'd like to put together a USB2 external raid enclosure but speed is concerning me.
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usb 2 throughput for external hard drives
- Thread starter sdadept
- Start date
It's rated at shared 480Mb/s (Mega-bit) per host burst speed, not sustained throughput. Original Firewire 400 (1394a) is rated at a sustained 400Mb/s and does quite well. Now you can get Firewire 800 (1394b) rated at 800Mb/s which is excellent. LaCie has a whole line of these externals.
USB2 get your around 25 (+-5MB) MB/s sustained. I'd be surprised if there were any faster enclosures than this.
There is likely no higher burst speed, since most mass-storage devices do not use the isochronous"mode" for sending data, since there is no guarantee on integrity or even delivery.
There is likely no higher burst speed, since most mass-storage devices do not use the isochronous"mode" for sending data, since there is no guarantee on integrity or even delivery.
yes, a good Firewire (even 400) enclosure is likely to outperfom the equivalent USB implementation.sdadept said:that's a good point, I hadn't thought of that. Most of the motherboards I've bought recently have firewire ports so that might be the right way to go.
so the usb2 speed just doesn't cut it for sustained throughput then?
http://enthusiast.hardocp.com/article.html?art=MTA3NCw0LCxoZW50aHVzaWFzdA==
Exactly. For further reference, also see http://en.wikipedia.org/wiki/Usb#USB_2.0_Hi-Speed_vs_FireWire
note paragraph three
note paragraph three
Also noteworthy is http://en.wikipedia.org/wiki/Usb#Technical_detailsdavidlem said:Exactly. For further reference, also see http://en.wikipedia.org/wiki/Usb#USB_2.0_Hi-Speed_vs_FireWire
note paragraph three
which explains the four data transfer modes. It is important to realize that the bulk x-fer -which is commonly used for block devices, since it is guaranteed delivery with data integrity check- does not allow for the fulle 480Mbit/s to be used. In order to achieve the 480Mbit rate, isochronous transfers need to be employed, which can be sent every "microframe". Bulk transfers can only happen every frame, which is -IIRC- every ms, micro-frames occur every 125 micro-seconds.